A fuel cell of this kind is shown in FIG. 15, FIG. 16 and FIG. 17 hereof.
Referring to FIG. 15, a fuel cell 100 of related art is made up of an electrolyte membrane 101, positive and negative electrode layers 102, 103 disposed on the front and rear sides of the electrolyte membrane 101, a positive electrode diffusion layer 104 disposed on the positive electrode layer 102, a negative electrode diffusion layer 105 disposed on the negative electrode layer 103, an oxygen gas passage 106 provided on the outer face of the positive electrode diffusion layer 104, and a hydrogen gas passage (not shown) provided on the outer face of the negative electrode diffusion layer 105.
Oxygen gas flows from a supply side 106a of the oxygen gas passage 106 to a discharge side 106b. 
As a result of oxygen gas flowing into the oxygen gas passage 106 and hydrogen gas flowing into the hydrogen gas passage, hydrogen (H2) is brought into contact with a catalyst in the negative electrode layer 103 and oxygen (O2) is brought into contact with a catalyst in the positive electrode layer 102, and a current is produced.
As shown in FIG. 16, hydrogen ions (H+) produced in a reaction in the negative electrode layer 103 (see FIG. 15) flow through the electrolyte membrane 101 to the positive electrode layer 102 as shown with an arrow.
And as a result of oxygen gas being supplied to the positive electrode layer 102 from the oxygen gas passage 106 (see FIG. 15), oxygen gas flows toward the electrolyte membrane 101 through the positive electrode layer 102.
Consequently, hydrogen ions (H+) and oxygen (O2) react and product water (H2O) is produced. The reaction between hydrogen ions (H+) and oxygen (O2) proceeds particularly in the area of the positive electrode layer 102 near its interface 108 with the electrolyte membrane 101, that is, in a ‘full catalytic reaction area’ 102a shown with dashed-line hatching.
Of the product water (H2O) produced, some product water returns to the electrolyte membrane 101 and keeps the electrolyte membrane 101 wet and thereby improves generation efficiency.
Of the remainder of the product water (H2O), some drains from inside the positive electrode layer 102 to the positive electrode diffusion layer 104 as shown by the arrow a, and the remainder of the product water (H2O) descends under its own weight through the inside of the positive electrode layer 102 as shown by the arrow b. Because of this, there is a tendency for product water (H2O) to collect at the bottom side 102b of the positive electrode layer 102, and this has been a hindrance to raising the generation efficiency of the fuel cell.
As shown in FIG. 17, oxygen gas is passed from the supply side 106a of the oxygen gas passage 106 to the discharge side 106b as shown with an arrow.
Of the product water (H2O) flowing out from the positive electrode layer 102 to the positive electrode diffusion layer 104, some product water evaporates and transpires into the oxygen gas passage and is carried by the oxygen gas in the oxygen gas passage 106.
Oxygen gas readily stagnates in the bends 106c, 106c of the oxygen gas passage 106, and the flow of oxygen gas in the discharge side 106b of the oxygen gas passage 106, that is, in the bottom side 102b of the positive electrode layer 102, tends to decrease.
Because of this, in the discharge side 106b of the oxygen gas passage 16, product water having transpired into the oxygen gas passage is not drained efficiently, product water tends to collect in the discharge side 106b, and this constitutes a hindrance to raising the generation efficiency of the fuel cell.
For example in JP-A-8-088008, a fuel cell is proposed wherein, to take account of the fact that the reaction between hydrogen ions (H+) and oxygen (O2) proceeds particularly in the ‘full catalytic reaction area’ 102a as shown in FIG. 16, the amount of electrolyte in the positive electrode layer is made greater on the electrolyte membrane side.
In this fuel cell, a large amount of electrolyte is included in the positive electrode layer 102 in the vicinity of its interface 108 with the electrolyte membrane 101, whereby it is possible to raise the conductivity of hydrogen ions (H+) at the interface 108 between the positive electrode layer 102 and the electrolyte membrane 101.
And for example in JP-A-2002-298859, a fuel cell is disclosed wherein, in view of the fact that stagnation of product water is a hindrance to raising generation efficiency, product water (H2O) is drained from inside the positive electrode layer 102 efficiently.
In this fuel cell, a water-repellent resin is included in the surface of the positive electrode layer 102 except in the bottom part 102b, so that product water flows out easily from the bottom part 102b and product water can be prevented from collecting in this bottom part 102b. 
Also, for example in JP-A-2002-042823, a fuel cell is disclosed wherein, to raise generation efficiency by keeping the electrolyte membrane 101 wet, the water content of the electrolyte membrane 101 is kept good.
In this fuel cell, drainage of product water is suppressed in the supply side 106a of the oxygen gas passage 106, and drainage of product water is promoted in the discharge side 106b of the oxygen gas passage 106, whereby it becomes possible to keep the water content of the electrolyte membrane good.
Here, to further widen the usability of the fuel cell in the industrial field, as well as raising the performance of the fuel cell it is important to keep down the cost of the fuel cell.
However, with only the measure of including a large amount of electrolyte in the vicinity of the interface with the electrolyte membrane, as in the fuel cell of JP-A-8-088008, it is difficult to further raise the performance of the fuel cell and lower the cost of the fuel cell.
And with only the measure of including a water-repellent resin in the surface of the positive electrode layer except in its bottom part, as in the fuel cell of JP-A-2002-298859, it is difficult to further raise the performance of the fuel cell and lower the cost of the fuel cell.
And with only the measure of suppressing the drainage of product water in the supply side of the oxygen gas passage and promoting the drainage of product water in the discharge side of the oxygen gas passage, as in JP-A-2002-042823, it is difficult to further raise the performance of the fuel cell and lower the cost of the fuel cell.
So, a fuel cell has been awaited which has excellent generation efficiency and with which it is possible to suppress cost.